The present invention relates to a high-frequency probe such that one end of a conductor is pressed to an electrode of a device-under-test (DUT) arranged on a device stage and the other end is connected to the external conductor through a coaxial connector connected to another end of this inner conductor. And in particular, the present invention relates to a high-frequency probe that makes it possible to measure the device not having a ground electrode on a surface of the device-under-test (DUT), to correspond to a device having narrowly-pitched electrodes or multiple pins, and to secure durability by simplification of point conciseness.
Conventionally, in this type of high-frequency probe, as shown in FIGS. 1A through 1C, and FIG. 2, at an end of a probe 100, a signal contact 101 and ground contacts 102 and 102A are contacted with three corresponding device electrodes arranged on the surface of the device-under-test (DUT) 120, which is called as coplanar type. These device electrodes are aligned in a row in the horizontal direction on the surface of the device-under-test (DUT) 120. Normally, as inner conductor 103 positioned in the center of the probe 100 becomes the signal contact 101, and contacts to a signal electrode 113 of the device-under-test (DUT) 120. In addition, a outer conductor 104 of the probe 100 is formed as ground contacts 102 and 102A on the left and right of the signal contact 101 at the end of the probe 100, and contacts to ground electrodes 118 of the device-under-test (DUT) 120.
As shown in FIG. 3, let thickness of the signal electrode 113 of the device-under-test (DUT) 120 be represented by "tsig" and let the thickness of the ground electrode 118 be represented by "tgnd". Usually, as shown in FIGS. 4A through 4C, combination of these thicknesses "tsig" and "tgnd" is "tsig=tgnd" (FIG. 4A), "tsig&gt;tgnd" (FIG. 4B), and "tsig&lt;tgnd" (FIG. 4C). This means that the end of the probe 100 must have elasticity since a uniform pressure amount is necessary for the signal electrode 113 and ground electrode 118 at the end of the probe 100.
Nevertheless, it is difficult to make a coaxial line of the probe 100 have the elasticity. Therefore, with using members having the elasticity as the inner conductor 103 and outer conductor 104, the signal contact 101 and ground contacts 102 and 102A are made to have the elasticity.
In this type of construction, the signal electrode and ground electrode of the device-under-test (DUT) should have the same arranged intervals as those of the probe contacts and should exist on the same plane as that of the probe contacts. Nevertheless, some probe contacts have such construction that the signal electrode and ground electrode are vertically aligned with defining a device stage as the reference ground against a case that the ground electrodes do not exist on the device surface, for example, they are on the back surface. In this case of longitudinal construction, so as to absorb unevenness of height of the device electrodes, a large vertically-movable range is necessary, and hence simple alignment cannot deal with this problem.
In addition, in case the ground electrodes and signal electrode are on a device surface and the arranged intervals of electrodes of a coplanar type device-under-test (DUT) are the same as those of the probe contacts, contact is possible. Nevertheless, distribution of electric force lines at the time of contact differs according to dispersion of electrode height, and in consequence, characteristic impedance of the probe varies. Hence, accurate measurement cannot be performed.
Although the impedance does not change due to electrode height (thickness) at the time of contact if end faces of the ground device electrodes of the device-under-test (DUT) is made to coincide with the end faces of the ground contacts, mutual alignment is difficult. From the viewpoint of the device side, since two ground electrodes should be provided for one signal electrode on the same plane so as to correspond to conventional probe contacts, the size of the device becomes large, and hence cost also increases.
In particular, compound devices such as GaAs devices have wafer cost more expensive than that of silicon. For this reason, in mass-production devices, both of cost reduction and security of high-frequency characteristics are realized by not providing ground electrodes on the same plane, making a chip area small and making wafer thickness thin, and assigning the back side to a ground electrode surface.
If the signal electrode and ground electrodes of the device-under-test (DUT) are apart from each other, the probe contacts can contact to them by making intervals of the probe contacts coincide with those of the device-under-test (DUT). Nevertheless, since the distance between the signal contact and ground contacts changes at an end part of the probe, impedance mismatching arises, and hence accurate measurement cannot be performed.
In order to reduce the influence of this mismatching, electrode length should be shortened. Nevertheless, so as to make the probe have the elasticity, the probe contacts should have some extent of length and thinness. By elongating the probe contacts, the characteristics get worse due to impedance mismatching. Furthermore, thin probe contacts are easily broken by overdrive at the time of contact.
On the other hand, since a body over from a coaxial connector positioning in a base part to the end part has predetermined size, this probe can be applied to device electrodes with inclining the probe against the plane so as to shorten the length of the relatively thin probe contacts. Nevertheless, since the probe contacts deeply bite into the device electrodes due to reduction of the elasticity and overdrive of the probe contacts, damage to the probe contacts becomes large.
In addition, usually, a device having a good high-frequency characteristic has a backside used as a whole-surface ground so as to obtain a good grounding characteristic. In particular, in LSIs (large scale integrated circuits) described later, line width becomes small, and hence the ground surface is approached to the signal lines on the surface by making the device thin so as to obtain a predetermined impedance characteristic, for example, 50.OMEGA.. In consequence, the ground electrodes are not on the same plane as that of the signal electrode, and the ground surface exists at a near position in the plane. Therefore, if the ground surface is formed on the whole surface of the backside, the probe having the above-described construction cannot contact.
In addition, conventional probe contacts have such structure that the ground electrode, signal electrode, and ground electrode are horizontally aligned in this order in the direction being perpendicular to the pressure direction at the time of contact to device electrodes. Therefore, this type of probe cannot deal with a case that signal electrodes are aligned in narrow pitches like those of LSI. Although probes that can deal with narrowly-pitched electrodes or multiple pins exist, the ground electrodes are not structurally stretched to the end of each probe. Therefore, since the impedance mismatching, crosstalk between signal electrodes, and the like arise, they cannot be used in high-frequency domains.
As described above, conventional high-frequency probes have the following problems.
A first problem is that correspondence is very difficult or impossible if the signal electrode and ground electrodes of a device-under-test (DUT) such as a microstrip type are not arranged in the same plane.
Its reason is that, since the probe contacts contacting to the device electrodes are horizontally aligned on the same plane and the pitches of the probe contacts coincide with the pitches of device electrodes in such alignment, the probe contacts cannot contact to the device electrodes not having this construction.
A second problem is that, if the signal electrode and ground electrodes of a device-under-test (DUT) such as a microstrip type are not on the same plane, accurate measurement is not performed even if electrode pitches of the device-under-test (DUT) are the same as those of the probe contacts and contact is possible.
Its reason is that the distribution of electric force lines at the time of contact differs according to the degree of unevenness of the device electrode and hence the characteristic impedance of the probe changes. In addition, another reason is that alignment of electrodes is difficult. Furthermore, still another reason is that the probe cannot contact to the device electrodes if the unevenness of the device electrodes exceeds the allowable value of overdrive.
A third problem is that the probes cannot deal with devices having such construction that narrowly-pitched multiple signal electrodes are aligned like those of LSI.
Its reasons are that the aligned order of electrodes of an LSI is not fixed to the order of the ground electrode, signal electrode, and ground electrode, and that pitches of the device electrodes also do not always coincide with the pitches of the probe contacts.